An antonym for this is a peak or a summit.
An antonym is the opposite term. The opposite of the base of the mountain would be the top. Another term for this would be the peak or the summit. You might also say the climax or the cap.
an antonym for that would be at the mountains base
base
Lowly, base.
base, headquarters.
the peak of the mountain
Ignoble: Base, unworthy.
base of a mountain
The antonyms for hammock are: Bed, hill, mountain, and sceres.
The base word of mountaineering is "mountain."
the oppposite OS the base of a mountain is the summit
Mountaintop, peak, summit.